With continuous innovations of electronic techniques and rapid developments of digital technologies, 3C information products have become indispensable outfits and helpful working tools for many people. 3C information products include notebook computers, mobile phones, personal digital assistants (PDAs), handheld computers (Palms) and the like. PDA, because of its powerful functions, user-friendliness and light and compact size, has been widely accepted by consumers. In addition, PDA can also include many other functions such as to access the Internet in a wireless fashion, communication, and video/audio enabling. It has become a prevailing trend of the information product development nowadays.
Refer to FIG. 1 for a conventional PDA. It includes a casing 10, a display panel 12, a direction key 14 and a plurality of hot keys 16. The casing 10 has a panel opening and a plurality of key openings formed on the surface to match and accommodate the display panel 12, the direction key 14 and the hot keys 16. The direction key 14 and the hot keys 16 are extended above the key openings. Users can depress the direction key 14 or the hot keys 16 to perform operations of the PDA. The information provided by the PDA are displayed on the display panel 12.
Referring to FIGS. 2A and 2B, the key structure adopted by conventional techniques for PDAs includes a direction key 21, a casing 22 and a circuit board 23. The casing 22 has a key opening 24 formed on the surface thereof. The direction key 21 consists of an outer key 25 and an inner key 26. The outer key 25 is slightly smaller than the key opening 24 while the inner key 26 is slightly larger than the key opening 24. Hence the outer key 25 is extended outside the key opening 24 while the inner key 26 is confined between the casing 22 and a circuit board 23. The key connects to the circuit board 23 through an elastic element 27 (such as a spring). The elasticity of the elastic element 27 enables the direction key 21 to turn and tilt at a small angle in four directions.
The direction key 21 has four indicating notations located on the four corners (up, down, left and right) of the outer key 25. The four bottom corners (up, down, left and right) of the inner key 26 has four contact points 28 corresponding respectively to four touch switches 29 located on the surface of the circuit board 23. When in use, users may select one of the notations and depress downwards, the direction key 21 is tilted at the depressing spot to make the contact point 28 in contact with the touch switch 29 of the circuit board 25. The PDA then process programs according to the commands input from the direction key 21. The processed results are displayed on the display panel (not shown in the drawings), and users may read the messages and information on the display panel.
These days, PDA equipped with video/audio or mobile phone capabilities has become an important feature. One of the critical elements to achieve the aforesaid functions is the speaker. To make the PDA competitive, it must be lean and light, and has a big enough display screen. To meet those requirements, conventional techniques of PDA have fully utilized the interior space of the casing for the configuration of the necessary elements or the arrangement of external keys. It is very difficult to allocate an additional space for the speaker. When trying to adopt the conventional techniques to add the speaker on the front side of the PDA without increasing the total size, the size of the display panel has to be shrunk. To keep the speaker on the front side of the PDA without reducing the size of the display panel, total size of the PDA should be increased. To install the speaker on the rear side of the PDA will increase the total thickness. Besides, when the speaker is located on the rear side of the PDA, the audio quality is not desirable. When it is coupled with the mobile phone, the voice output from the rear side has the risk of being eavesdropped.
Because of the conventional techniques have difficulty to include the speaker in the PDA and still meet the requirements of lean and light and a large enough display screen, it is necessary to develop new techniques to resolve the problem.